Search for neutral long-lived particles in $pp$ collisions at $\sqrt{s}=13$ TeV that decay into displaced hadronic jets in the ATLAS calorimeter

The collaboration
JHEP 06 (2022) 005, 2022.

Abstract (data abstract)
A search for decays of neutral long-lived particles (LLPs) is presented using 139/fb of proton-proton collisions data collected by the ATLAS detector at the LHC in 2015--2018 at a center-of-mass energy of 13 TeV. Dedicated techniques are developed in this search for the reconstruction of displaced jets produced by LLPs decaying hadronically in the ATLAS hadronic calorimeter. Two search regions are defined for different LLP kinematic regimes. The observed numbers of events are consistent with the expected background and limits for several benchmark signals are determined. For a scalar boson with a mass of 125 GeV, branching ratios above 10% are excluded at 95% confidence level for LLP proper decay lengths in the range between 2 cm and 10 m depending on the model. Upper limits are also set on the cross-section times branching ratio for heavy scalars with a mass of 60 GeV and for masses between 200 GeV and 1 TeV.

• #### Table 1

Data from Table 1

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CalRatio triggers which were available during the LHC Run 2 data-taking, and corresponding integrated luminosity collected in each period. The...

• #### Figure 2a

Data from Figure 2a

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Trigger efficiency for simulated signal events as a function of the LLP pT for one of the low-ET signal samples...

• #### Figure 2b

Data from Figure 2b

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Trigger efficiency for simulated signal events as a function of the LLP pT for one of the high-ET signal samples...

• #### Figure 3a

Data from Figure 3a

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Trigger efficiency for simulated signal events as a function of the LLP decay position in the x–y plane (Lxy) for...

• #### Figure 3b

Data from Figure 3b

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Trigger efficiency for simulated signal events as a function of the LLP decay position in the x–y plane (Lxy) for...

• #### Figure 5a

Data from Figure 5a

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The NN output scores in the dijet control region for the low-ET training with no adversary network. Statistical uncertainties are...

• #### Figure 5b

Data from Figure 5b

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The NN output scores in the dijet control region for the low-ET training with an adversary network included. Statistical uncertainties...

• #### Figure 5c

Data from Figure 5c

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The NN output scores in the dijet control region for the high-ET training with no adversary network. Statistical uncertainties are...

• #### Figure 5d

Data from Figure 5d

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The NN output scores in the dijet control region for the high-ET training with an adversary network included. Statistical uncertainties...

• #### Figure 7a

Data from Figure 7a

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Distribution of the low-ET per-event BDT in main data, BIB data and some of the benchmark signal samples after preselection....

• #### Figure 7b

Data from Figure 7b

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Distribution of the high-ET per-event BDT outputs in main data, BIB data and some of the benchmark signal samples after...

• #### Table 3 Top

Data from Table 3 Top

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Sequential impact of each requirement on the number of events passing the selection for the high-ET selections. The signal columns...

• #### Table 3 Bottom

Data from Table 3 Bottom

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Sequential impact of each requirement on the number of events passing the selection for the low-ET selections. The signal columns...

• #### Table 4 Top

Data from Table 4 Top

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Application of the modified ABCD method to the final high-ET selections. The a priori estimate refers to the "pre-unblinding" case,...

• #### Table 4 Bottom

Data from Table 4 Bottom

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Application of the modified ABCD method to the final low-ET selections. The a priori estimate refers to the "pre-unblinding" case,...

• #### Figure 10a

Data from Figure 10a

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95% CL expected and observed limits on the BR of SM Higgs bosons to pairs of neutral LLPs (BH→ ss),...

• #### Figure 1a of Aux. Mat.

Data from Figure 1a of Aux. Mat.

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Trigger efficiency of simulated signal events as a function of the LLP decay position in the z direction for LLPs...

• #### Figure 1b of Aux. Mat.

Data from Figure 1b of Aux. Mat.

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Trigger efficiency of simulated signal events as a function of the LLP decay position in the z direction for LLPs...

• #### Figure 2a of Aux. Mat. 60_5

Data from Figure 2a of Aux. Mat. 60_5

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The simulated efficiencies as a function of c times the mean proper lifetime (cτ) of s for several different MC...

• #### Figure 2a of Aux. Mat. 60_16

Data from Figure 2a of Aux. Mat. 60_16

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The simulated efficiencies as a function of c times the mean proper lifetime (cτ) of s for several different MC...

• #### Figure 2b of Aux. Mat. 125_5

Data from Figure 2b of Aux. Mat. 125_5

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The simulated efficiencies as a function of c times the mean proper lifetime (cτ) of s for several different MC...

• #### Figure 2b of Aux. Mat. 125_16

Data from Figure 2b of Aux. Mat. 125_16

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The simulated efficiencies as a function of c times the mean proper lifetime (cτ) of s for several different MC...

• #### Figure 2b of Aux. Mat. 125_35

Data from Figure 2b of Aux. Mat. 125_35

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The simulated efficiencies as a function of c times the mean proper lifetime (cτ) of s for several different MC...

• #### Figure 2b of Aux. Mat. 125_55

Data from Figure 2b of Aux. Mat. 125_55

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The simulated efficiencies as a function of c times the mean proper lifetime (cτ) of s for several different MC...

• #### Figure 2c of Aux. Mat. 200_50

Data from Figure 2c of Aux. Mat. 200_50

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The simulated efficiencies as a function of c times the mean proper lifetime (cτ) of s for several different MC...

• #### Figure 2c of Aux. Mat. 400_100

Data from Figure 2c of Aux. Mat. 400_100

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The simulated efficiencies as a function of c times the mean proper lifetime (cτ) of s for several different MC...

• #### Figure 2d of Aux. Mat. 600_50

Data from Figure 2d of Aux. Mat. 600_50

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The simulated efficiencies as a function of c times the mean proper lifetime (cτ) of s for several different MC...

• #### Figure 2d of Aux. Mat. 600_150

Data from Figure 2d of Aux. Mat. 600_150

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The simulated efficiencies as a function of c times the mean proper lifetime (cτ) of s for several different MC...

• #### Figure 2d of Aux. Mat. 600_275

Data from Figure 2d of Aux. Mat. 600_275

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The simulated efficiencies as a function of c times the mean proper lifetime (cτ) of s for several different MC...

• #### Figure 2e of Aux. Mat. 1000_50

Data from Figure 2e of Aux. Mat. 1000_50

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The simulated efficiencies as a function of c times the mean proper lifetime (cτ) of s for several different MC...

• #### Figure 2e of Aux. Mat. 1000_275

Data from Figure 2e of Aux. Mat. 1000_275

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The simulated efficiencies as a function of c times the mean proper lifetime (cτ) of s for several different MC...

• #### Figure 2e of Aux. Mat. 1000_475

Data from Figure 2e of Aux. Mat. 1000_475

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The simulated efficiencies as a function of c times the mean proper lifetime (cτ) of s for several different MC...

• #### Figure 4a of Aux. Mat.

Data from Figure 4a of Aux. Mat.

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The event BDT in the dijet control region for the low-ET training training. The uncertainties are combined statistical and ML...

• #### Figure 4b of Aux. Mat.

Data from Figure 4b of Aux. Mat.

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The event BDT in the dijet control region for the high-ET training. The uncertainties are combined statistical and ML modelling...

• #### Figure 5a of Aux. Mat.

Data from Figure 5a of Aux. Mat.

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The 95% CL observed limits, expected limits and ± 1 σ and 2 σ bands for the Φ mass of...

• #### Figure 5b of Aux. Mat.

Data from Figure 5b of Aux. Mat.

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The 95% CL observed limits, expected limits and ± 1 σ and 2 σ bands for the Φ mass of...

• #### Figure 5c of Aux. Mat.

Data from Figure 5c of Aux. Mat.

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The 95% CL observed limits, expected limits and ± 1 σ and 2 σ bands for the Φ mass 125...

• #### Figure 5d of Aux. Mat.

Data from Figure 5d of Aux. Mat.

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The 95% CL observed limits, expected limits and ± 1 σ and 2 σ bands for the Φ mass 125...

• #### Figure 5e of Aux. Mat.

Data from Figure 5e of Aux. Mat.

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The 95% CL observed limits, expected limits and ± 1 σ and 2 σ bands for the Φ mass 125...

• #### Figure 5f of Aux. Mat.

Data from Figure 5f of Aux. Mat.

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The 95% CL observed limits, expected limits and ± 1 σ and 2 σ bands for the Φ mass of...

• #### Figure 6a of Aux. Mat.

Data from Figure 6a of Aux. Mat.

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The 95% CL observed limits, expected limits and ± 1 σ and 2 σ bands for the Φ mass of...

• #### Figure 6b of Aux. Mat.

Data from Figure 6b of Aux. Mat.

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The 95% CL observed limits, expected limits and ± 1 σ and 2 σ bands for the Φ mass 600...

• #### Figure 6c of Aux. Mat.

Data from Figure 6c of Aux. Mat.

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The 95% CL observed limits, expected limits and ± 1 σ and 2 σ bands for the Φ mass of...

• #### Figure 6d of Aux. Mat.

Data from Figure 6d of Aux. Mat.

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The 95% CL observed limits, expected limits and ± 1 σ and 2 σ bands for the Φ masses of...

• #### Figure 6e of Aux. Mat.

Data from Figure 6e of Aux. Mat.

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The 95% CL observed limits, expected limits and ± 1 σ and 2 σ bands for the Φ masses of...

• #### Figure 6f of Aux. Mat.

Data from Figure 6f of Aux. Mat.

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The 95% CL observed limits, expected limits and ± 1 σ and 2 σ bands for the Φ masses of...

• #### Figure 6g of Aux. Mat.

Data from Figure 6g of Aux. Mat.

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The 95% CL observed limits, expected limits and ± 1 σ and 2 σ bands for the Φ masses of...

• #### Figure 11 of Aux. Mat.

Data from Figure 11 of Aux. Mat.

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Efficiency for an event to enter Region A of the high-ET selection, as a function of the two LLP kinematics,...

• #### Figure 12 of Aux. Mat.

Data from Figure 12 of Aux. Mat.

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Efficiency for an event to enter Region A of the low-ET selection, as a function of the two LLP kinematics,...

Version 2 modifications: Added additional resource: neural network preserved in ONNX format.